This invention is an optical array converting UV radiation, especially contained in sunlight. The spectral characteristic of the transmission of the filter is similar to the sensitivity of human skin to sun burning. That sensitivity is described by the widely recognized Diffey Standard, also called also the Erythema Action Spectrum.
The Roberston Berger UV meter has been widely used over the past two decades to measure UV in good approximation of the Diffey/Erythemal Spectral Response. This stationary device is based on a phosphore convertor screen as the principle means to reach a spectral response close to the Erythemal/Diffey Curve.
By now there are a few UV hand-held measuring devices known on the market that are targeting monitoring of LTV radiation for avoiding sunburning. CASIO Computer Ltd. manufactures a device called xe2x80x9cCASIO UC-120 UVxe2x80x9d, which has an optical array containing absorptive filter made of material similar to Schott UG-11 and a photodiode. The spectral characteristic of the device doesn""t match the Diffey Standard. The device illuminated by sunlight is too sensitive to UV-A, that has low burning power.
U.S. Pat. No. 5,196,705 describes a device measuring the intensity and dose of UV. The device has an optical array containing: an absorptive filter made of material similar to Schott UG-11, a photo-luminescentive material and a photodiode. The spectral characteristic of the device doesn""t match the Diffey Standard. The device is too sensitive to UV-A comparing to its sensitivity to UV-B.
Several others solutions for biologically oriented monitors of UV radiation were also proposed, among them:
U.S. Pat. No. 5,036,311 describes a UV-monitoring system in which a light sensing element is placed under a curved optical element with interference filters imposed on its surface.
U.S. Pat. No. 5,401,970 describes a UV-monitoring device which incorporates a UV-B sensor and a VIS sensor. The UV-B detector involved is described to be based on a phosphor convertor screen.
The invention solves the problem of constructing a device equipped with an optical array converting UV, visible and IR radiation that has the spectral characteristic of the transmission similar to the Diffey Standard. Definition of the relative internal transmission of a set of filters:
Trelint(xcex)=Tint(xcex)/Tint(310)xe2x80x83xe2x80x83(1)
where:
Note that the total internal transmission of the set of absorptive filters is equal to the product of internal transmissions of each consecutive filter.
Definition of the relative transmission of a set of filters:
Trel(xcex)=T(xcex)/T(310)xe2x80x83xe2x80x83(2)
The Diffey spectral characteristics will be denoted as D(xcex) (3) where:
In the first solution the array contains a system of absorptive filters to block visible and IR radiation, a system of interference filters modifying transmission of UV and/or blocking visible and IR radiation, scattering elements, elements forming the light beam. Interference filter/filters is/are made of layers of materials having high and low UV refractive indexes. According to the invention one of the system of interference filters has layers made of Hafnium oxide and/or Zirconium oxide. A collimator placed in the optical path forms the light beam. The collimator can have surfaces highly absorbing light. At the beginning of the optical path a scatterer is placed to achieve non-directional characteristic of the array. The scatterer can be made of PTFE.
In the second solution the array contains the first system of absorptive filters to partly block UV-A, the second system of absorptive filters to block visible and IR radiation and may contain scattering elements and/or system/systems of interference filter/filters. The first system of absorptive filters has internal relative transmission Trelint(xcex): between 0 and 0.2 for xcex=290 nm, between 0.34 and 0.7 for xcex=300 nm, between 0.5 and 0.8 for xcex=320 nm, between 0.04 and 0.36 for xcex=330 nm, between 10E-3 and 0.1 for xcex=340 nm, between 7*10E-6 and 0.02 for xcex=350 nm, between 2*10E-7 and 7*10E-3 for xcex=360 nm, between 2*10E-7 and 7*10E-3 for xcex=370 nm, between 2*10E-5 and 0.03 for xcex=380 nm, between 2*10E-3 and 0.14 for xcex=390 nm. The total optical thickness of the first system of absorptive filters is between 0.5 and 2 mm.
The second system of absorptive filters has internal relative transmission Trelint(xcex): between 0 and 0.3 for xcex=290 nm, between 0.7 and 0.8 for xcex=300 nm, between 1 and 1.3 for xcex=320 nm, between 1 and 1.4 for xcex=330 nm, between 1 and 1.3 for xcex=340 nm, between 1 and 1.12 for xcex=350 nm, between 0.6 and 0.8 for xcex=360 nm, between 0.14 and 0.3 for xcex=370 nm, between 10E-3 and 0.015 for xcex=380 nm, between 10E-10 and 10E-6 for xcex=390 nm. The total optical thickness of the first system of absorptive filters is between 0.5 and 10 mm.
At the beginning of the optical path a scatterer is placed to achieve non-directional characteristic of the array. The scatterer can be made of PTFE. In the optical path additional system/systems of interference filters can be placed to block visible and IR radiation and/or to modify transmission in UV range.
This invention allows producing a cheap and simple optical array with a spectral characteristics in the UV-A and TV-B range following the human skin sensitivity described by Diffey Standard. The scatterer ensures non-directional characteristics of the array. Other standards of skin sensitivity to UV-A and UV-B burning can also be easily followed.